Here to say that I am having the same problems. Lost connection twice today….
Broadcast HR is absolutely related or can at least exacerbate the problem. I can reproduce the issue easily by having my Whoop 5.0 connect to my Garmin Edge to stream HR, upon completing my activity with Garmin, the Whoop consistently loses connection to my phone. Can reproduce with 2 different Whoop devices and 2 different Garmin devices. Clearly some sort of BT connection bug.
**** UPDATE 2 ******
I have a partial pattern. Anytime the band is out of touch with the phone or Bluetooth is turned off, it won’t reconnect once it’s within proximity of the phone or Bluetooth is turned back on. The way I get it to reconnect is go to the Bluetooth list, unpair the 5MG and within 15 seconds I get a pop up asking if I would like to reconnect to the device. I HOPE THEY FIX THIS SOON.